1. Field of the Invention
The invention relates to radio frequency identification (RFID) readers, and in particular, to RFID reader antennas.
2. Background Art
Radio frequency identification (RFID) tags are electronic devices that may be affixed to items whose presence is to be detected and/or monitored. The presence of an RFID tag, and therefore the presence of the item to which the tag is affixed, may be checked and monitored wirelessly by devices known as “readers.” Readers typically have one or more antennas transmitting radio frequency signals to which tags respond. Since the reader “interrogates” RFID tags, and receives signals back from the tags in response to the interrogation, the reader is sometimes termed as “reader interrogator” or simply “interrogator”.
With the maturation of RFID technology, efficient communication between tags and interrogators has become a key enabler in supply chain management, especially in manufacturing, shipping, and retail industries, as well as in building security installations, healthcare facilities, libraries, airports, warehouses etc.
The requirements for RFID readers are becoming more difficult to meet. RFID readers require an antenna that possesses proper gain, produces a desired antenna pattern, and produces a properly polarized signal. Furthermore, the antenna must provide a very low Voltage Standing Wave Ratio (VSWR), which equates to a very low RF return loss. These properties must be maintained over a considerably wide frequency bandwidth, even though the antenna may be aimed at large and highly reflective objects in the vicinity of the tags intended to be read. Reflections due to these objects can create difficulties in properly reading the tags.
Furthermore, reading of tags often takes place in an environment where the reader antenna experiences physical abuse, such as in a warehouse environment, where objects may impact the reader antenna.
Thus, what is needed are RFID reader antennas that have sufficient gain, and can produce a useful antenna pattern, with proper polarization. Furthermore, the antennas should have a low VSWR, to provide for a low RF return loss. Still further, the antennas need to be capable of operating in an environment having highly reflective objects, and should be rugged to withstand environmental abuse.